# Tag Info

10

The rubber sheet only is not meant to be a qualitative model, it gives one concept and one concept only: Mass causes curvature of spacetime. You can't get any more than that from the rubber sheet. If you have that idea in your head already then you are ready to drop the image because: The sheet is 2d but spacetime is 4d The 2d sheet is embedded in 3d ...

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I just wrote an answer about this. The rubber sheet is a good model of 2D Newtonian gravity, with a 1/r force law. If you make a rigid surface in the shape of the 3D gravitational potential, like the gravity wells you find in some science museums, and roll small balls on it, it's a pretty good model of orbits in 3D Newtonian gravity, with the correct 1/r2 ...

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Yes. Gravitational wave observatories like the proposed eLISA laser interferometer may be able to detect gravitational waves that originate from the early moments of the big bang itself. If some part of the big bang energy goes into gravitational waves then those waves will be redshifted by expansion and waves produced in the first $<10^{-10}$ s should be ...

3

There shouldn't be any correlation. The CMB light that we see is from a spherical region in the early universe. Its homogeneity strongly suggests that the interior of the sphere was just as homogeneous, but we can't actually see CMB light from the interior. The galaxies that we can see formed from matter inside the sphere, and quite far from the edge. ...

3

CMB fluctuations The CMB fluctuations are often analyzed through their power spectrum $P(k)$, which is a measure of the extent to which it is "clumpy" on a given scale $\ell$, with corresponding wavenumber $k = 2\pi/\ell$. The origin of this power spectrum is laid in the very early early Universe, just after the Big Bang, and it is of utmost ...

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An appropriate explanation might begin by explaining that the cosmic microwave background (CMB) was formed in the expanding universe about 400,000 years after the big bang. An expanding gas cools, and when the gas in the universe cooled to about 3000 K, a transition tok place whereby the protons and electrons, hitherto free particles, combined to form ...

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The comoving radius of the sphere of matter that we see as the CMBR can be calculated from measured cosmological parameters, and is around 46 billion light years. The comoving size encompassed by our past light cone back to the beginning of time is not known, but it has to be much larger—at least hundreds of billions of light years across, and potentially ...

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The peaks in the temperature and polarization spectra determine the angular size of the sound horizon at the time of recombination fairly accurately: $$\theta = \frac{r}{D(z)}$$ The sound horizon, which is represented by r, is the comoving distance a sound wave could travel from the beginning of the universe to recombination and is a standard ruler is any ...

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Some extensive search e.g. with scholar.google.com led me to a manuscript from October 2020 entitled Design and Characterization of 275-500 GHz Corrugated Horns and Optics for a Wideband Radio Astronomy Receiver which already has all the information in the title: It looks like there is current development towards another 500 GHz receiver. The question ...

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